Method for controlling storage device controller, storage device controller, and program

ABSTRACT

Disclosed herein is a method for controlling a storage device controller connected to a storage device provided with a plurality of storage volumes for storing data respectively and an information processing apparatus for requesting an input/output of data so as to receive an input/output request from the information processing apparatus and execute an input/output processing of the data for each of the plurality of storage volumes. The method brings one (primary) of the plurality of storage volumes into correspondence with another (secondary) in which a copy of data is to be written when the data is written in the primary volume so as to form a pair group consisting of a plurality of pairs, each having such a primary volume and such a secondary volume. Upon receiving an input/output request from the information processing apparatus, the method starts resetting of the correspondence between storage volumes of each pair included in the pair group to decide whether or not it is after resetting of the correspondence is started that the request has been issued and executes an input/output processing after resetting the correspondence if the request is issued after resetting of the correspondence is started.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority upon Japanese Patent ApplicationNo. 2002-366374 filed on Dec. 18, 2002, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a storagedevice controller, a storage device controller, and a program.

2. Description of the Related Arts

There is a well-known copy management function used in a storage systemthat includes an information processing apparatus and a disk array unitconnected to each other for communications. The function manages primaryvolume data in duplicate by copying data from a primary volume to asecondary volume in real time. The primary (master) volume that is asource of copy and the secondary (sub) volume that is a destination ofcopy are paired.

In such a storage system, however, data often overflows one primaryvolume into other primary volumes during communications between theinformation processing apparatus and the disk array unit. If an attemptis made to back up the data in such an occasion, a plurality of pairs(of primary and secondary volumes) must be reset from the paired state.If data in a primary volume for which the pair is already reset isupdated during sequential resetting of paired states, the data is notupdated in its corresponding secondary volume while data in a primaryvolume of which pair state is not reset is updated in its correspondingsecondary volume sometimes.

SUMMARY OF THE INVENTION

Under such circumstances, it is an object of the present invention toprovide a method for controlling a storage device controller, a storagedevice controller, and a program capable of managing copies of datawhile keeping the consistency among the data stored in a plurality ofstorage volumes.

One aspect of the present invention resides in the storage devicecontrolling method that controls the storage device controller connectedto a storage device provided with a plurality of storage volumes forstoring data and an information processing apparatus for requesting theinput/output of the data and used to input/output the data to/from thestorage volumes. The method comprises a step of bringing one (source) ofthe storage volumes into correspondence with another (destination) inwhich a copy of data is to be written when the data is written in thesource storage volume so as to form a pair group consisting of aplurality of such source and destination storage volumes; a step ofresetting the correspondence between source and destination storagevolumes of each pair in the pair group; a step of deciding whether ornot it is after the correspondence is reset that an input/output requesthas been issued from the information processing apparatus; and a step ofinputting/outputting data after the correspondence is reset when it isafter the correspondence is reset that the input/output request has beenissued from the information processing apparatus.

The storage device and the storage device controller are included in thedisk array unit. The information processing apparatus and the disk arrayunit are included in the storage system.

Storage volumes are storage resources provided in the disk array unit orstorage device and they are divided into physical volumes and logicalvolumes. A physical volume is a physical storage area provided in a diskdrive of the disk array unit or storage device and a logical volume is astorage area allocated logically in a physical volume.

The “paired” means a state in which two storage volumes are brought intocorrespondence with each other as described above.

That is why the present invention can provide a method for controlling astorage device controller, a storage device controller, and a programcapable of managing copies of data while keeping the consistency amongdata stored in a plurality of storage volumes as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described inconjunction with the accompanying drawings, in which:

FIG. 1 is an overall block diagram of a storage system in an embodimentof the present invention;

FIG. 2 is a block diagram of an information processing apparatus in theembodiment of the present invention;

FIG. 3 is a block diagram of a channel adapter provided in a storagedevice controller in the embodiment of the present invention;

FIG. 4 is a table stored in a shared storage provided in the storagedevice controller in the embodiment of the present invention;

FIG. 5 is pairs of storage volumes in the embodiment of the presentinvention;

FIG. 6 is a flowchart of the processings of the storage devicecontroller for splitting a pair in the embodiment of the presentinvention;

FIG. 7 is a flowchart of the processings of the storage devicecontroller for splitting a pair and inputting/outputting the split pairdata items in the embodiment of the present invention;

FIG. 8 is a table stored in the shared storage provided in the storagedevice controller in the embodiment of the present invention; and

FIG. 9 is a flowchart of the processings of the storage devicecontroller for splitting a pair.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

===Overall Configuration===

At first, the storage system in an embodiment of the present inventionwill be described with reference to the block diagram shown in FIG. 1.

An information processing apparatus 100 is a computer provided with aCPU (Central Processing Unit), a memory, etc. The CPU of the informationprocessing apparatus 100 executes various types of programs to realizevarious functions of the apparatus 100. The information processingapparatus 100 is used, for example, as a core computer in an automaticteller machine in a bank, a flight ticket reservation system, or thelike.

The information processing apparatus 100 is connected to a storagedevice controller 200 to communicate with the controller 200. Theinformation processing apparatus 100 issues data input/output commands(requests) to the storage-device controller 200 to read/write datafrom/to the storage devices 300. The information processing apparatus100 also sends/receives various commands to/from the storage devicecontroller 200 to manage the storage devices 300. For example, thecommands are used for managing copies of data stored in the storagevolumes provided in the storage devices 300.

FIG. 2 shows a block diagram of the information processing apparatus100.

The information processing apparatus 100 is configured by a CPU 110, amemory 120, a port 130, a media reader 140, an input device 150, and anoutput device 160.

The CPU 110 controls the whole information processing apparatus 100 andexecutes the programs stored in the memory 120 to realize variousfunctions of the apparatus 100. The media reader 140 reads programs anddata recorded on the recording medium 170. The memory 120 stores theprograms and data read by the reader 140. Consequently, the media reader170 can be used to read a storage device management program 121 and anapplication program 122 recorded in the medium 170 and store them in thememory 120. The recording medium 170 may be any of flexible disks,CD-ROM disks, semiconductor memories, etc. The media reader 140 may alsobe built in the information processing apparatus 100 or provided as anexternal device. The input device 150 is used by the operator to inputdata addressed to the information processing apparatus 100. The inputdevice 150 may be any of keyboards, mice, etc. The output device 160outputs information to external. The output device 160 may be any ofdisplays, printers, etc. The port 130 is used to communicate with thestorage device controller 200. In that connection, the storage devicemanagement program 121 and the application program 122 may be receivedfrom another information processing apparatus 100 through the port 130and stored in the memory 120.

The storage device management program 121 manages copies of data storedin the storage volumes provided in the storage devices 300. The storagedevice controller 200 manages copies of data with use of various copymanagement commands received from the information processing apparatus100.

The application program 122 realizes the functions of the informationprocessing apparatus 100. For example, the program 122 realizesfunctions of an automatic teller machine of a bank and functions of aflight ticket reservation system as described above.

Next, the storage device controller 200 will be described with referenceto FIG. 1 again. The storage device controller 200 controls the storagedevices 300 according to the commands received from the informationprocessing apparatus 100. For example, when receiving a datainput/output request from the information processing apparatus 100, thestorage device controller 200 inputs/outputs data to/from a storagevolume provided in a storage device 300.

The storage device controller 200 is configured by a channel adapter210, a cache memory 220, a shared storage 230, a disk adapter 240, amanagement terminal (SVP: SerVice Processor) 260, and a connection unit250.

The channel adapter 210 provided with a communication interface with theinformation processing apparatus 100 exchanges data input/outputcommands, etc. with the information processing apparatus 100.

FIG. 3 shows a block diagram of the channel adapter 210.

The channel adapter 210 is configured by a CPU 211, a cache memory 212,a control memory 213, a port 215, and a bus 216.

The CPU 211 controls the whole channel adapter 210 by executing acontrol program 214 stored in the control memory 213. The controlprogram 214 stored in the control memory 213 thus enables data copies tobe managed in this embodiment. The cache memory 212 stores data,commands, etc. to be exchanged with the information processing apparatus100 temporarily. The port 215 is a communication interface used for thecommunication with the information processing apparatus 100 and otherdevices provided in the storage device controller 200. The bus 216enables the mutual connection among those devices.

Return to FIG. 1 again. The cache memory 220 stores data to be exchangedbetween the channel adapter 210 and the disk adapter 240 temporarily. Inother words, if the channel adapter 210 receives a write command as adata input/output command from the information processing apparatus 100,the channel adapter 210 writes the command in the shared storage 230 andthe target data received from the information processing apparatus 100in the cache memory 220 respectively. The disk adapter 240 then readsthe target data from the cache memory 220 according to the write commandwritten in the shared storage and writes the read data in a storagedevice 300.

The management terminal 260 is a kind of information processingapparatus used for the maintenance/management of the storage devicecontroller 200 and the storage devices 300. For example, the managementterminal 260 changes the control program 214 executed in the channeladapter 210 to another. The management terminal 260 may be built in thestorage device controller 200 or may be separated. The managementterminal 260 may also be dedicated to the maintenance/management of thestorage device controller 200 and the storage devices 300 or may beconfigured as a general information processing apparatus formaintenance/management. The configuration of the management terminal 260is the same as that of the information processing apparatus 100 shown inFIG. 2. Concretely, the management terminal 260 is configured by a CPU110, a memory 120, a port 130, a recording media reader 140, an inputdevice 150, and an output device 160. Consequently, the control programto be executed in the channel adapter 210 may be read from the recordingmedium 170 through the media reader 140 of the management terminal 260or received from the information processing apparatus 100 connectedthereto through the port 130 of the management terminal 260.

The disk adapter 240 controls the storage devices 300 according to thecommands received from the channel adapter 210.

Each of the storage devices 300 is provided with a storage volume to beused by the information processing apparatus 100. Storage volumes arestorage resources provided in the storage devices 300 and divided intophysical volumes that are physical storage areas provided in disk drivesof the storage devices 300 and logical volumes that are storage areasallocated logically in those physical volumes. The disk drives may beany of, for example, hard disk drives, flexible disk drives,semiconductor storage devices, etc. The disk adapter 240 and each of thestorage devices 300 may be connected to each other directly as shown inFIG. 1 or through a network. The storage devices 300 may also be unitedwith the storage device controller 200 into one.

The shared storage 230 can be accessed from both of the channel adapter210 and the disk adapter 240. The shared storage is used to receive/senddata input/output requests/commands and store management information,etc. of the storage device controller 200 and the storage devices 300.In this embodiment, the shared storage 230 stores a consistency groupmanagement table 231 and a pair management table 232 as shown in FIG. 4.

===Pair Management Table===

The pair management table 232 is used to manage copies of data stored inthe storage devices 300. The table 232 has columns of “pair”, “primaryvolume”, “sub volume”, “pair state”, and “consistency group”.

The “pair” column holds pair names. A pair means a combination of twostorage volumes. FIG. 5 shows an example of paired storage volumes. InFIG. 5, two pairs, that is, pairs A and B are denoted. One of pairedvolumes and the other of the paired volumes are managed as a primaryvolume and a secondary volume. In FIG. 5, a primary volume is describedas a master volume and a secondary volume is described as a sub volume.A plurality of secondary volumes can be combined with one primaryvolume.

Return to the pair management table 232 shown in FIG. 4. The “primary”column describes primary volumes paired with secondary volumes while the“secondary” column describes secondary volumes paired with primaryvolumes.

The “pair state” column describes the state of each pair of volumes. The“pair state” is classified into “paired”, “split”, and “re-sync”.

The “paired” denotes that data in a secondary volume is updated with thedata in its corresponding primary volume written by the informationprocessing apparatus 100. The consistency of the data stored in a pairof primary and secondary volumes is assured with such correspondence setbetween those primary and secondary volumes.

The “split” denotes that data in a secondary volume is not updated withthe data in its corresponding primary volume written by the informationprocessing apparatus 100. Concretely, while primary and secondaryvolumes are in such a “split” state, the correspondence between thosevolumes is reset. Consequently, the data consistency is not assuredbetween those primary and secondary volumes. However, because data inany secondary volume that is in the “split” state is not updated, thedata in secondary volumes can be backed up during the while; forexample, data stored in secondary volumes can be saved in a magnetictape or the like. This makes it possible to back up data while the datain primary volumes is used continuously during the backup operation fora job that has been executed by the information processing apparatus100.

The “re-sync” denotes a transition state of a pair of volumes, forexample, from “split” to paired”. More concretely, the “re-sync” means astate in which data in a secondary volume is being updated with the datawritten in its corresponding primary volume while the pair is in the“split” state. When the data in the secondary volume is updated, thestate of the pair is changed to “paired”.

To form a pair of storage volumes or to change the state of the pairfrom “paired”/“split” to “split”/“paired”, the operator instructs theinformation processing apparatus 100 in which the storage devicemanagement program 121 is executed through the input device 150. Acommand from the operator is then sent to the channel adapter 210 of thestorage device controller 200. After that, the channel adapter 210executes the control program 214 to form a pair of storage volumes orchange the state of the pair according to the command. According to thestate of the formed pair of storage volumes, the channel adapter 210controls the object storage volumes, for example, updating a secondaryvolume with a copy of data updated in its corresponding primary volumewhen those volumes are “paired”.

As described above, the channel adapter 210 changes the states of pairsone by one sequentially. This is because one primary volume can bepaired with a plurality of secondary volumes as described above and ifthe states of a plurality of pairs are changed simultaneously, themanagement of primary volumes comes to become complicated.

Forming a pair of volumes and changing the state of each pair of volumescan also be made automatically at a predetermined time or according to acommand received from another information processing apparatus 100connected through the port 130 independently of instructions from theoperator.

===Consistency Group===

The “consistency group” column describes the number of each consistencygroup (pair group) consisting of pairs of volumes. A consistency groupmeans a group of a plurality of storage volume pairs to be controlled sothat the states of those pairs are changed to the “split” together.Concretely, a plurality of pairs in a consistency group are controlledso that their states are changed to the “split” simultaneously(hereinafter, this processing will be referred to as the synchronismamong the state changes to the “split”) while the states of a pluralityof paired volumes are changed one by one sequentially as describedabove.

For example, assume now that the information processing apparatus 100writes data in a storage volume while the pair states of a plurality ofpaired volumes in a consistency group are changed sequentially from“paired” to “split”. If no consistency group is formed and the data iswritten in a paired primary volume after the pair state is changed tothe “split”, the data is not written in its corresponding secondaryvolume. If the data is written in a paired primary volume of which stateis not changed to the “split” yet, the data is also written in thesecondary volume. If the paired primary volume belongs to a consistencygroup at that time, however, the data is not written in itscorresponding secondary volume regardless of the pair state of theprimary volume (whether it is in the “split” or not). This is becausethe data is written in the primary volume after pair splitting(resetting of the correspondence between primary and secondary volumes)is started in the consistency group.

Forming a consistency group with a plurality of pairs such way iseffective for a case in which data is to be stored in a plurality ofstorage volumes, for example, when write data is too large to be storedin one storage volume and when it is controlled so that one file data isstored in a plurality of storage volumes.

Such assured synchronism of the pair state changes of volumes to the“split” in a consistency group is also effective for writing/reading ofdata in/from secondary volumes requested from the information processingapparatus 100.

Concretely, if no consistency group is already formed, data can bewritten/read in/from any paired secondary volume after the pair state ischanged to the “split” while it is inhibited to write/read data in/fromany secondary volume of which pair state is not changed to the “split”.

In this embodiment, a batch split receiving flag (ID information) of theconsistency group management table 231 is used to assure the synchronismof such pair state changes of volumes to the “split” in the aboveconsistency group. Next, the processings for assuring such synchronismwill be described with reference to the flowchart shown in FIG. 6.

Processing Flow

The following processings are executed by the CPU 211 provided in thechannel adapter 210 with use of the control program 214 (program)consisting of codes for realizing various operations in this embodiment.

At first, the channel adapter 210 receives a pair splitting request(split command) addressed to a consistency group from the informationprocessing apparatus 100(S1000). The channel adapter 210 then turns onthe batch split receiving flag in the consistency group management table231 stored in the shared storage 230 (S1001). After that, the channeladapter 210 begins to change the pair state of a not-split pair ofvolumes in the consistency group to the “split” (S1003). Concretely, thechannel adapter 210 resets the correspondence between the primary volumeand the secondary volume in the pair and stops updating of the data inthe secondary volume with the data written in the primary volume. Thechannel adapter 210 then changes the description for the pair in the“paired” column in the pair management table 232 to “split” (S1004).Those processings are repeated for each pair in the consistency group.When the states of all the pairs in the consistency group are changed tothe “split” (S1005), the channel adapter 210 turns off the batch splitflag, then exits the processing.

If the channel adapter 210 receives a read/write request from theinformation processing apparatus 100 during the above processing, theadapter 210 checks whether or not the request is addressed to anot-split storage volume, that is, a “paired” storage volume (for whichthe correspondence to its secondary volume is not reset)(S1006). If thecheck result is YES (addressed), the adapter 210 changes the pair stateof the volume to the “split” (S1007). The adapter 210 then changes thedescription of the pair in the pair state column in the pair managementtable 232 to the “split” (S1008) and executes the data read/writeprocessing (input/output processing)(S1009).

On the other hand, if the check result in (S1006) is NO (not addressed),this means that the command is addressed to a “split” volume. Theadapter 210 thus executes the read/write processing for the storagevolume (S1009) immediately.

Consequently, the synchronism of the pair state changes of “paired”volumes to the “split” in a consistency group is assured.

In the flowchart shown in FIG. 6, if the channel adapter 210 receives aread/write request from the information processing apparatus 100 whilesplitting paired volumes in a consistency group sequentially, theadapter 210 checks whether or not the request is addressed to anot-split pair of volumes (S1006) to execute the read/write processing(S1009). However, it is also possible for the adapter 210 to suppressthe execution of the read/write processing requested from theinformation processing apparatus 100 while the adapter 210 splits pairedvolumes in a consistency sequentially. In that connection, the adapter210 can execute the read/write processing after the adapter 210completes splitting of all the paired volumes in the consistency groupand turns off the batch split flag.

FIG. 7 shows a flowchart for those processings by the channel adapter210 in detail.

At first, the channel adapter 210 forms a consistency group for bothpairs A and B according to a command received from the informationprocessing apparatus 100(S2000 to S2002). The command is inputted, forexample, by the operator through the input device 150 of the informationprocessing apparatus 100. The command inputted to the informationprocessing apparatus 100 is sent to the channel adapter 210 by thestorage device management program 121. The “paircreate-g GRP0” shown inFIG. 7 is such a command. Receiving the command, the channel adapter 210forms a consistency group, then records predetermined data in the pairmanagement table 232 and the consistency group management table 231stored in the shared storage 230 respectively. FIG. 4 shows how thepredetermined data is recorded in those tables 231 and 232. However,although the state of the pair A is described as “split” in the pairstate column in the pair management table 232 shown in FIG. 4, the stateof the pair A at that time is actually “paired”. Similarly, although“ON” is described in the batch split receiving flag column for theconsistency group 0 in the consistency group management table 231, theactual state at that time is actually “OFF”.

The channel adapter 210, when receiving a read/write request (R/W1) forthe storage volume 1 in the pair A from the information processingapparatus 100(S2008), executes the read/write processing as usually(S2009). This is because “OFF” is described in the batch split receivingflag column for the consistency group 0 in the consistency groupmanagement table 231.

After that, the information processing apparatus 100 instructs thechannel adapter 210 to split the pair B in the consistency group 0 witha command (S2003). The “pairsplit-g GRP0” shown in FIG. 7 is an exampleof the command issued at that time. This command may also be inputted bythe operator through the input device 150 of the information processingapparatus 100.

The channel adapter 210 then turns on the batch split receiving flag forthe consistency group 0 in the consistency group management table 231stored in the shared storage 230 (S2004) to start splitting of each pairsequentially (S2005, S2006). FIG. 4 shows the pair management table 232in which the pair A is split. Completing splitting of all the targetpairs, the channel adapter 210 turns OFF the batch split receiving flagand exits the processing (S2007).

If the channel adapter 210 receives a read/write request (R/W2)addressed to the storage volume 3 of the pair B from the informationprocessing apparatus 100 (S2010) while the channel adapter 210 turns ONthe batch split receiving flag (S2004) after receiving a split commandaddressed to the consistency group 0 from the information processingapparatus 100, the channel adapter 210 executes the read/writeprocessing as usually (S2011). This is because “OFF” is still set in thebatch split receiving column for the consistency group 0 in theconsistency group management table 231.

However, if the channel adapter 210 receives a read/write request (R/W3)addressed to the storage volume 3 of the pair B from the informationprocessing apparatus 100 (S2012) after turning ON the batch splitreceiving flag (S2004), the channel adapter 210 splits the pair B(S2013), then executes the read/write processing (S2014).

As described above, the channel adapter 210, when receiving a read/writerequest from the information processing apparatus 100, refers to thebatch split receiving flag to check whether or not it is after resettingof the pair state of each pair in the consistency group is started thatthe read/write command has been issued.

If the channel adapter 210 receives the read/write request (R/W4) aftercompleting splitting of the pair A in (S2005), the channel adapter 210executes the read/write processing (S2016). This is because “split” isset for the pair A in the pairing column in the pair management table232 and the channel adapter 210 knows that “split” denotes that the pairA is split.

In that connection, no splitting processing is done for the pair B in(S2005), since the pair B is already split during the read/writeprocessing in (S2013).

In this embodiment, because the batch split receiving flag is providedas described above, the synchronism among the pair state changes of allthe pairs in a consistency group to the “split” is assured.

===Consistency Group Management Table===

Next, a description will be made for another embodiment of the presentinvention with respect to the management information in the consistencygroup management table 231.

In this embodiment, each split starting time is recorded in theconsistency group management table 231 as shown in FIG. 8. In theexample shown in FIG. 8, splitting of pairs in the consistency group 0is started at 12:00. When splitting of all the pairs in the consistencygroup 0 is completed, the description in the split starting time columnis changed to “-”.

A split starting time is specified with a command received from theinformation processing apparatus 100. Such split starting may also bespecified so as to be started immediately with a command; no concretetime is specified in such an occasion. In that connection, the currenttime is recorded in the split starting time column.

In this embodiment, the channel adapter 210, when receiving a read/writecommand from the information processing apparatus 100, compares theread/write command issued time recorded in the read/write command(request) with the time described in the split starting time column ofthe consistency group management table 231. If the command issued timeis later, the channel adapter 210 executes the read/write processingafter the end of the splitting.

This is why it is possible to assure the synchronism among the statechanges of pairs in a consistency group to the “split”.

===Processing Flow===

Next, how the above processings are executed will be described in detailwith reference to the flowchart shown in FIG. 9.

The processings are executed by the CPU 211 of the channel adapter 210with use of the control program 214 consisting of codes for realizingvarious operations in this embodiment.

At first, the channel adapter 210 receives a pair splitting request(split command) addressed to a consistency group from the informationprocessing apparatus 100 (S3000). The channel adapter 210 then recordsthe split starting time recorded in the split command in the splitstarting time column of the consistency group management table 231stored in the shared storage 230 (S3001). After that, the channeladapter 210 compares the split starting time with the current time tocheck whether or not the split starting time is passed (S3003). If thecheck result is YES (passed), the channel adapter 210 begins the statechange of a not-split pair in the consistency group to the “split”(S3004). Concretely, the channel adapter 210 resets the correspondencebetween primary and secondary volumes of the pair and suppressesupdating of the data in the secondary volume with the data written inthe primary volume. The channel adapter 210 then changes the descriptionfor the pair in the pair state column in the pair management table 232to “split” (S3005). The above processings are repeated for all of thepairs in the consistency group. When the states of all the pairs in theconsistency group are changed to “split” (S3006), the channel adapter210 changes the description for the pair in the split starting timecolumn to “-” and exits the processing (S3007).

If the channel adapter 210 receives a read/write request from theinformation processing apparatus 100 during the above processing, thechannel adapter 210 checks whether or not the request is addressed to anot-split pair, that is, a “paired” storage volume (the correspondenceis not reset)(S3008). If the check result is YES (addressed), thechannel adapter 210 compares the command issued time recorded in thecommand with the split starting time (S3010). If the command issued timeis later, the channel adapter 210 changes the pair state to the “split”(S3011), then changes the description for the pair in the pair statecolumn in the pair management table 232 to “split” (S3012). After that,the channel adapter 210 executes the read/write processing (input/outputprocessing) (S3013).

On the other hand, if the read/write command is addressed to a splitpair in (S3008), that is, a “split” storage volume or the command issuedtime recorded in the request is earlier than the split starting time,the channel adapter 210 reads/writes data from/in the storage volume(S3009).

This is why it is possible to assure the synchronism among the statechanges of the pairs in a consistency group to the “split”.

In the flowchart shown in FIG. 9, if the channel adapter 210 receives aread/write request from the information processing apparatus 100 whilesplitting pairs in a consistency group sequentially, the channel adapter210 checks whether or not the request is addressed to a not-splitstorage volume (S3008) and executes the read/write processing (S3009,S3013). However, the channel adapter 210 can also suppress execution ofthe read/write processing even when receiving a read/write request fromthe information processing apparatus 100 while splitting pairs in aconsistency group sequentially as described above. In that occasion, thechannel adapter 210 executes the read/write processing after completingsplitting of all the pairs in the consistency group and changing thedescription for the pair in the split starting time column to “-”.

In this embodiment, consistency groups are formed by storage devices 300connected to the same storage device controller respectively. However,the present invention is not limited only to that embodiment. In thisembodiment, consistency groups should preferably be formed by storagedevices 300 connected to a plurality of storage device controllersrespectively. In that connection, a consistency group may be formed overa plurality of storage device controllers 200 that come to communicatewith each another to create the consistency group management table 231and the pair management table 232. The consistency group managementtable 231 and the pair management table 232 may be managed by one of thestorage device controllers 200 and shared with other storage devicecontrollers 200 or each of those storage device controllers manages thesame table. Furthermore, volumes controlled by a plurality of storagedevice controllers 200 should preferably be paired in this embodiment.In that connection, a pair might be formed over a plurality of storagedevice controllers 200 and those storage device controllers 200 come tocommunicate with each another to create the consistency group managementtable 231 and the pair management table 232. In that connection, theconsistency group management table 231 and the pair management table 232may be managed by one of the storage device controllers 200 and sharedwith other storage device controllers 200 or those storage devicecontrollers manages the same table respectively.

While the embodiments of the present invention have been described, thedescription is just for illustrative purposes, and it is to beunderstood that changes and variations may be made without departingfrom the spirit or scope of the following claims.

1. A method for controlling a storage device controller; wherein thecontroller is connected to a storage device provided with a plurality ofstorage volumes for storing data respectively and an informationprocessing apparatus for requesting an input/output of the data so as toreceive the input/output request and input/output the data to/from eachof the plurality of storage volumes; wherein the method comprises thesteps of: bringing one (source) of the plurality of storage volumes intocorrespondence with another (destination) in which a copy of data is tobe written when the data is written in the source volume so as to form apair group consisting of a plurality of such pairs of the source volumeand the destination volume respectively; resetting the correspondencebetween storage volumes of each pair included in the pair group;deciding whether or not it is after the correspondence is reset that theinput/output request is issued from the information processingapparatus; and executing the input/output processing after resetting thecorrespondence when the input/output request is issued from theinformation processing apparatus after the correspondence is reset.2-12. (canceled)